1. Field of the Invention
The present invention relates to a film antenna which is integrated into a chassis of a mobile terminal such as a notebook PC, or the like, and particularly, to a film antenna whose resonance frequency, even when it is fitted into a chassis formed of metal, can be preadjusted without being affected by the chassis.
2. Description of the Related Art
In mobile terminals such as notebook PCs, PDAs, etc., wireless LANs (IEEE 802.11a/b/g) have become increasingly common.
The standards of these wireless LANs are 802.11a which uses a band of 5 GHz, and 802.11b/g which uses a band of 2.4 GHz. As an antenna for wireless LANs, a planar antenna which is capable of dual-band oscillation in these bands of 2.4 GHz and 5 GHz has been demanded.
For example, as conventional planar antennae, Japanese patent application laid-open No. 2003-152429 discloses a planar antenna in which a ground portion and a radiating element portion are formed by the die-cutting of a lead frame, and Japanese patent application laid-open No. 2003-8325 discloses an antenna device in which an inverted-F antenna is formed of conductor films formed on both sides of an insulative substrate.
These antennae are housed by attaching them with a two-sided tape or the like to the back side of a peripheral frame of a mobile terminal display or the back side of a cover on a body side. However, since the display and body cover are provided with a metal chassis, there is the problem that, when an antenna is attached close to the metal chassis, it is affected by the metal chassis to cause a variation in resonance frequency. For this reason, to maintain antenna characteristics, an antenna is attached spaced a constant distance or greater apart from a metal chassis that is grounded, as shown in Japanese patent application laid-open Nos. 2002-99352 and 2002-232220. However, there is extreme difficulty in attaching the antenna to a narrow mobile terminal without affecting antenna characteristics, which, in practice, requires tuning by adjusting, for example, the length of the antenna element for each mobile terminal to which it is attached.
In particular, since a thin thickness has recently been required, and magnesium, aluminum, etc. have been used for chassis, there is difficulty in attaching the antenna spaced sufficiently apart from the metal chassis. Accordingly, there is the problem that, because a resonance frequency is significantly varied according to attachment position, antenna design must be performed taking account of chassis structure and attachment position, so that the antenna cannot be used for different models without modification.
Further, since antenna attachment is performed by using a two-sided tape, high-precision attachment to a fixed position cannot be ensured.